The present invention is generally related to radio frequency (RF) signal couplers, and more particularly to an embedded transmission line coupler for RF signal amplifiers of cellular telephones.
In conventional cellular telephones, RF signal couplers have been implemented by several methods, including by means of capacitive couplers or transmission line couplers. Prior transmission line couplers typically have been designed to be terminated by fifty ohm loads at all ports. As a result, it is necessary to include circuitry in the output of an RF signal amplifier that provides a match to a fifty ohm load. Such output matching circuitry usually includes one or more transmission lines and several capacitors, resistors and/or inductors, all of which require valuable circuit board space. Furthermore, the overall insertion loss between the RF signal amplifier and the antenna includes losses due to both the output matching circuitry and the transmission line coupler. For the foregoing reasons, there is a need for an embedded transmission line coupler that is integrated into the output matching circuitry of the RF signal amplifier.